Apple II+ disk drive problems

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Apple II+ disk drive problems

I have an Apple II+, and a compact floppy disk drive with an Apple II disk interface card.

First, a description of a previous problem:
I have had problems with the Apple not booting if the disk interface card is plugged in. It seemed like the card's PROM is sucking power through the data bus due to internal clamping diodes. The PROM's +5V supply is disconnected when the /I/O SELECT signal is inactive (high), so I tried bypassing the circuit so that the PROM is always powered (this is not a good idea when using many peripheral cards but I had only the disk interface card). This worked much better, as the drive now lights up and spins when powering the Apple. I should perhaps mention that I've replaced a failing 8T28 transceiver with a 74HC245, which I guess could be part of the problem.

This is the current problem:
Now I cannot properly boot the Apple with a DOS 3.3 disk I have. It seems like the Apple reads for a few seconds, then exits with something like this:

*9D10 A=34 X=10 Y=35 S=9A

That's NOT the exact output, just a general idea of how it looks. I don't have access to the Apple right now (at work!). I think the disk is OK, but I'm gonna test it when I get my hands on the Apple IIe I have elsewhere...

So my questions are:
1) why is the Apple not working properly when disk interface card is plugged in?
2) what is the meaning of the output I get when trying to boot DOS, and how do I fix it?
3) what should the Apple do when there is no disk in the disk drive? does it spin endlessly?

Peace
Jakob

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Re: Apple II+ disk drive problems

I have an Apple II+, and a compact floppy disk drive with an Apple II disk interface card.

I take it to mean this is a non-Apple drive? I don't recall them making a "compact." But there were lots of aftermarket drives.

First, a description of a previous problem:
I have had problems with the Apple not booting if the disk interface card is plugged in. It seemed like the card's PROM is sucking power through the data bus due to internal clamping diodes.

I'll have to take your word for that one. Wink

It seems like the Apple reads for a few seconds, then exits with something like this:

*9D10 A=34 X=10 Y=35 S=9A


Ok, it read a track or two, tried to run the DOS that it found on the drive, and ran into a BRK instruction. Something got lost in the translation from the floppy through the disk drive electronics through the Disk ][ card to your computer.

I think the disk is OK, but I'm gonna test it when I get my hands on the Apple IIe I have elsewhere...

That will be important to rule out what's at fault.

So my questions are:
1) why is the Apple not working properly when disk interface card is plugged in?

Could be faulty electronics, out-of-spec drive rotation speed, or a dirty read head.

2) what is the meaning of the output I get when trying to boot DOS, and how do I fix it?

It's a machine language program gone bad. You fix it by finding out what's at fault and replacing it: the drive, the drive card, or the floppy disk containing DOS.

3) what should the Apple do when there is no disk in the disk drive? does it spin endlessly?

Yes, a Disk ][ card will spin the drive endlessly after knocking the head on the stepper motor stop several times (to seek track 0).

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Doing the easy things first c

Doing the easy things first clean the head of the disk. Try booting a known good disk. Everything mentioned above in the previous post should be helpful. If you can boot a known good disk. Then if you have Copy II+ newer versions that let you check the drive speed on a BLANK disk. Not sure if you trying to boot a dat disk.

Maybe the the drive alginment and the disks tracks do not match. It might have been made with a drive that was slightly out of specs.

Take Care,

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I just tested moving the driv

I just tested moving the drive + floppy disk to my Apple IIe and everything works as it should there, and DOS 3.3 boots after a few seconds Smile

Therefor I am starting to suspect that the problem is the electrical specs for the 74HC245 I am using instead of 8T28 being outside limits when reading from disk drive. Is there somewhere I can get a hold of a few 8T28's, or are there any other transceiver IC's I can use?

EDIT: seems like the NTE 6889 is a compatible IC, and I have ordered one from mouser. I'll get back when I have tried it.

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